There is a clinical need in fixed prosthodontics for indirect esthetic materials that are biologically compatible, wear and fatigue resistant, tough, strong, and can be easily processed into thin layers and complex shapes for use in veneering teeth and restoring large defects in much the same manner as cast gold. Metal-ceramics, ceramics and thermoset based composites are all being used with increased frequency to satisfy the esthetic demands that cast metal alone no longer can. Metal-ceramics have become the treatment of choice for the complete coverage restoration of extensively broken down anterior and posterior teeth. While the clinical longevity of metal-ceramic is good, the major drawbacks of these restorations is considered to be the increased amount of tooth reduction which is required to achieve often only adequate esthetics. Dental ceramics have outstanding chemical durability and stability, optical and biologic compatibility and have done much to improve the esthetic quality of dental restorations. The principle drawback of all ceramic materials, however, is their inability to deform without fracture. The use of thermoset resin matrix composites for indirect restorative procedures has been advocated by some clinicians but the optical stability and performance of these materials in high stress bearing areas such as posterior occlusal surfaces and anterior incisal edges remains suspect. High performance restorative materials with the optical stability of ceramic and the clinical longevity of metals and metal-ceramics are the long range goals of this study. The thermoset resin matrix of current dental composites has been implicated as being contributory to the poor clinical performance of the material with respect to color stability, wear resistance and toughness. Thermoplastic resin matrix composite materials art a relatively new class of materials and have been used for a number of high performance structural applications often as a substitute for metals, ceramics and thermoset composites. Thermoplastic polymers with improved water and chemical resistance, wear resistance and toughness have been selected for evaluation as the matrix phase of particulate reinforced composites. There is clearly a lack of information available to assess the performance of such materials. This proposal is designed to evaluate four particulate reinforced thermoplastic resin matrix composites for potential use as indirect restorative materials. A commercial composite (Herculite XR, Kerr) will act as the control and the filler type will remain constant for all materials. Wear resistance, fatigue and fracture toughness will be the principal comparative measures and the effect of matrix properties on the composite performance will be assessed.